Everyday, organic waste streams are created that need to be treated in some form or manner before they are disposed of. For example, organic waste streams in conventional municipal waste and wastewater plants, food manufacturing facilities, industrial factories, and animal farms are typically treated either physically, chemically, and/or biologically before combining the effluent(s) with a water body, land applying the effluent(s), or disposing of the effluent(s) in an alternative manner, such as by removal from the site for further treatment elsewhere.
Organic waste treatment technologies have progressed significantly in recent years due, in part, to increased public awareness, lobbying, legislation and regulatory oversight. In some instances, treatment technologies have been developed upon the realization that entirely new and useful products could be created from the wastes thereby generating new business opportunities for technology innovators. Often times, new or improved technologies are created for purely economic reasons.
Presently, most treatment technologies for organic wastes typically include some form of biological treatment wherein biological organisms stabilize organic matter and remove soluble and/or nonsettleable colloidal solids to reduce the content of microbial substrates (nutrients such as phosphorus, sulfur and particularly nitrogen and other organic biodegradable materials as measured by the total biochemical oxygen demand (BOD) test). The microbial substrates, particularly if left untreated, are known to pollute surface and subsurface water supplies and negatively impact air and soil quality. Suspended growth processes, attached-growth processes and combined suspended and attached growth processes are used for biological treatment of organic wastes to reduce substrate quantities in the treated effluents. Often times, waste streams and the microbial substrates therein are also subjected to additional treatment processes prior to the disposal of process effluents such as, for example, screening, digestion, composting, disinfection, chemical precipitation, and/or phosphorus removal.
With increasing human population density, municipal wastewater treatment facilities, animal farming facilities, and industrial and food processing treatment facilities have come under increasing pressure to upgrade, modify, or supplement their treatment processes to improve the quality of system effluent discharges as well as the air in and around such facilities to further protect the environment, and human and animal health. A particularly persistent problem addressed by the present invention is the treatment of animal excrement containing high concentrations of microbial substrates which, in typical animal treatment systems, not only pollute surface and subsurface water supplies, but also negatively impact air and soil quality. The effluent discharges from these animal treatment systems oftentimes contain undesired amounts of available nitrogen and phosphorus which have been linked to detrimental effects in water bodies such as, for example, accelerated eutrophication and aquatic growths. Further, present treatment alternatives for organic waste streams, such as animal excrement, frequently generate and exacerbate the offensive odors and emissions of atmospheric pollutants.
The input to an organic waste biological treatment process usually contains concentrations of phosphorus and other nutrients such as, for example, nitrogen. This will hold for flowable organic waste streams or for non flowable wastes, such as scrapped fresh manure, which are converted into an aqueous stream by mixing with a recycle stream from a treatment process. For municipal wastewaters, the typical influent phosphorus (P) to nitrogen (N) load ratio (the “P/N Ratio”) is about 0.18. Metcalf & Eddy, Wastewater Engineering—Treatment and Reuse, 4th Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (2003). P/N Ratios for animal farm wastes are typically about 0.18 (dairy) to 0.30 (swine and layer chickens). ASAE Standard D384.1, 2003. Industrial waste and food industry waste P/N Ratios are less consistent than those for municipal or animal wastes and largely depend on the products and the processes. Some of the nutrients in such organic inputs will be incorporated into the microbial cell mass as a result of the biological treatment process and may be removed from treatment systems as a component of the solids (sometimes referred to as sludge). The portion of the nutrients remaining in the waste stream (whether converted or unconverted by the biological treatment process) will be discharged with the liquid effluent.
In some processes, the amount of a single nutrient can be a limiting factor to the biological treatment process and nearly all of that nutrient is converted and incorporated into the microbial cell mass leaving little, if any, portion of that nutrient in the process liquid effluent. In conventional biological wastewater treatment processes where the BOD and COD concentrations are not limiting, and when the P/N Ratio is appropriately low relative to the requirements of normally growing microbial populations, the vast majority of the phosphorus will be assimilated into biomass and the phosphorus in the liquid effluent will in turn be relatively low. This will generally be true if the P/N Ratio is less than about 0.16 (as long as no significant nitrification and denitrification is occurring in the system in which case nitrogen gas is typically released increasing the P/N Ratio that can be treated), since this is the P/N Ratio commonly found in slowly growing microbial cells. In effect, the phosphorus and nitrogen in the wastewater treatment system is assimilated into microbial cells.
In the low oxygen organic waste biologically mediated conversion system for an organic waste described in U.S. Pat. No. 6,689,274 (Northrop, et al.), in order to accomplish a similar result for biological conversion of phosphorus and nitrogen, the P/N Ratio needs to be somewhat lower than about 0.16 because significant amounts of nitrogen are discharged to atmosphere as dimolecular nitrogen gas and hence is not available for incorporation into microbial cells. Thus, P/N Ratios of about 0.07 or less would normally be required in the organic influent waste stream to achieve equivalent low effluent phosphorus discharges as seen in conventional biological treatment systems. The phosphorus content in the treated effluent depends upon the incorporation of phosphorus into microbial cells and other settleable and/or suspended solids and then separating those cells and solids from that effluent by collecting them as a portion of the harvested humus material generated by the process. Any phosphorus not converted into insoluble and/or particulate form, as well as any insoluble and/or particulate nutrients not collected in the harvested humus material will be discharged in the system effluent. On average, phosphorus removal by biological treatment processes with sludge wasting may range from 10 to 30 percent of the influent amount. Metcalf & Eddy, Wastewater Engineering, Treatment, Disposal, Reuse, 3rd Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (1991) at p. 726. According to the process described in U.S. Pat. No. 6,689,274, low effluent discharges of phosphorus would contain less than about 50 percent of the influent phosphorus load (greater than about 50 percent removal). Preferable discharges would contain less than about 20 percent of the influent phosphorus load (greater than about 80 percent removal).
When the influent waste stream to a biological wastewater treatment process contains P/N Ratios which are higher, sometimes substantially higher, than 0.16, the resulting concentration of soluble phosphorus in the effluent stream may be higher than desired and it is sometimes necessary and/or desirable to lower such effluent phosphorus discharges. One method known in the art to try to lower such effluent phosphorus discharges is the addition of an anaerobic zone to an aerobic wastewater biological treatment process. The expected increase in the phosphorus content of the resultant biomass and sludge is supposed to reduce effluent phosphorus discharges. This phosphorus conversion process is generally known as the “Bio-P” process and the conversion mechanism is understood to be as follows:
A community of micro organisms referred to as Phosphorus Accumulating Organisms (“PAOs”), when exposed to alternating aerobic and anaerobic environments, will take up excess amounts of phosphate ions and store them as polyphosphate. When these PAOs encounter anaerobic conditions they will use the energy stored in the polyphosphate, thereby decreasing their polyphosphate stores, and will accumulate acetate or other volatile fatty acids, storing these compounds in polymer form, usually as polyhydroxybuteric acid. When these organisms then encounter aerobic conditions they will oxidize the stored organic polymers and other energy sources using electron acceptors (e.g. oxygen) from the aerobic environment and use the energy to form energy rich polyphosphate. The polyphosphate is stored so that the energy it contains may be used when anaerobic conditions recur, which allows the PAOs to displace other heterotrophic microorganisms that can not take advantage of the stored energy to thrive under anaerobic conditions. This relative energy advantage in the anaerobic environment leads to the dominance of PAOs over other phosphate uptake organisms which utilize oxygen as an electron acceptor. See Janssen, P. M. J., Biological Phosphorus Removal, Manual for design and operation, IWA Publishing (2002) at p. 17. When the PAOs use the energy stored in the polyphosphate in the anaerobic sub-zone, soluble phosphorus is released. When the PAOs return to the aerobic zone soluble phosphorus is absorbed and again converted to polyphosphate removing it from the aqueous phase and incorporating it as insoluble or particulate microbial biomass. If this biomass is then removed under aerobic conditions before the anaerobic environment is encountered, the phosphorus is removed from the system. Metcalf & Eddy, Wastewater Engineering—Treatment and Reuse, 4th Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (2003) at p. 623-627.
Recently, the Bio-P mechanism has been found to work if the aerobic process is replaced with an anoxic process containing nitrate and/or nitrite instead of molecular oxygen. Janssen, P. M. J., Biological Phosphorus Removal, Manual for design and operation, IWA Publishing (2002) at p. 16. However, the efficiency of the process using an anoxic environment instead of an aerobic environment is lower than that obtained when molecular oxygen in an aerobic environment is used. This occurs because it takes energy to extract oxygen from electron acceptors such as nitrate or nitrite and so the net production of usable energy from a substrate must be decreased by this amount (usually by about 40 percent when the electron acceptor is nitrate, see Janssen at pg. 20).
Despite this reduced efficiency, the addition of an anaerobic environment to a nitrate containing anoxic process, and the recycling of the anoxic liquid through the anaerobic environment, allows denitrifying PAOs to have a similar Bio-P selective advantage over normal, non-PAO denitrifiers. However, prior to the Applicants' discovery, this selective advantage was expected to disappear as the concentration of nitrate decreased to low levels because, compared to a normal non-PAO denitrifier, it would become more difficult for the PAO to acquire the additional electron acceptors it needs to generate the extra energy required to build and use the various PAO polymers. Thus, the concentration of nitrate or nitrite is rate limiting for PAO denitrifiers at significantly higher levels than it is for normal non-PAO denitrifiers.
This rate limiting effect from concentrations of nitrate or nitrite is not a problem if other electron acceptors are available in sufficient quantities in the aerobic or anoxic environment. However, in environments with low electron acceptor concentrations, a cell would be less likely to get the additional ions it needs to grow and function compared to a normal denitrifier, and hence would not be competitive with such normal denitrifiers in that environment. The selective advantage which the anaerobic environment provided for PAO's would disappear. As the whole system approaches the conditions of an anaerobic environment (lower and lower concentrations of electron acceptors) the advantage of a separate anaerobic environment would be expected to disappear.
Despite the expectation that low concentrations of nitrate would make anoxic Bio-P ineffective, applicants have surprisingly found that if an anaerobic zone is added to or within the low oxygen organic waste bioconversion system described in U.S. Pat. No. 6,689,274 (Northrop et al.), and if the process liquid is recycled through the system, including the anaerobic zone, a significant transformation occurs whereby more soluble phosphorus is converted into particulate phosphorus. This transformation of soluble phosphorus into particulate form occurs even though the concentrations of molecular oxygen, nitrate, and nitrite are very low.
Even more surprising has been the discovery that once the transformation occurs, whereby more soluble phosphorus is converted into particulate phosphorus in a system which experiences alternating exposure to anaerobic and low electron acceptor environments, this enhanced phosphorus conversion (transforming into particulate form) ability can persist even when the anaerobic environment is subsequently removed from the process.
Thus, applicants have surprisingly discovered that certain populations of PAOs, and especially certain populations of denitrifying PAOs, can continue to accumulate significant levels of particulate phosphorus even when living in environments which have low concentrations of electron accepting substances (such as oxygen, nitrite, nitrate) and that these populations of PAOs maintain this conversion ability whether they function exclusively in low electron acceptor environments or whether they live in environments which vary between anaerobic and low electron acceptor conditions at either a microscopic or macroscopic scale.
In general, denitrifying PAOs are not expected to have a selective advantage to grow in low electron acceptor environments without a physically separated and defined anaerobic environment. However, Applicants have determined that the surprising ability to do so can be induced in a variety of ways that include, but are not limited to: 1. recycling the denitrifying PAOs between anaerobic and low electron acceptor zones containing relatively high phosphorus to nitrogen ratios (greater than about 0.16 and as high as about 0.3 to 0.5) until the phosphorus conversion ability is developed and then removing the anaerobic zone from the system, 2. seeding the low electron acceptor environment described in U.S. Pat. No. 6,689,274 and U.S. application Ser. No.10/600,936 containing relatively high phosphorus to nitrogen ratios (greater than about 0.16 and as high as about 0.3 to 0.5) with nitrifying and denitrifying PAOs which already are adapted to grow in the low electron acceptor environment without a physically separated and defined anaerobic environment, perhaps from another treatment system or from a PAO production site; and 3. in a system without a physically defined anaerobic environment but with a low electron acceptor environment, through varying low concentrations of electron acceptors in local zones (microenvironments) of a large environment containing relatively high phosphorus to nitrogen ratios (greater than about 0.16 and as high as about 0.3 to 0.5) so that a population of denitrifying PAOs evolves which is tolerant to and will grow in any such low electron acceptor environment as evidenced by particulate phosphorus concentrations.
There is clearly a competitive advantage for denitrifying PAOs which are able to grow exclusively in low electron acceptor environments and which can also grow in environments which have both low electron acceptor zones and anaerobic zones (microenvironments). Incorporation of these populations into organic waste treatment systems with relatively high phosphorus to nitrogen ratios allows such waste streams to be successfully treated within low electron acceptor environments without the necessity of designing, building, and operating additional systems or subsystems with discrete anaerobic environments. Capital investments are decreased, maintenance costs are reduced and land use is minimized.
Applicants have therefore discovered an improved process for the biologically mediated conversion of organic waste and removal of nutrients from the waste. This process operates at low electron acceptor concentrations while maintaining high quantities of diverse populations of microorganisms in the process. The present invention addresses many of the problems associated with municipal, domestic, industrial, food industry, animal husbandry and other organic wastes, by providing an attractive and efficient means to resolve ecological problems associated with the treatment of organic wastes. The present invention addresses the odor emission problem common to organic wastes as well as the problem associated with high nutrient effluent discharge concentrations through the efficient, substantially odorless, biologically mediated conversion of waste excrement materials or a vast array of other organic wastes into stable, economically and/or ecologically beneficial materials.
Thus, it is an object of the present invention to provide an improved process for the efficient, substantially odorless, biological treatment of organic waste.
It is another object of the present invention to provide an improved process for the efficient, substantially odorless, biological treatment of organic waste which converts a substantial portion of the soluble phosphorus into particulate form.
It is another object of the present invention to provide an improved process to create a biologically active, ecologically beneficial, substantially odorless humus material through the biologically mediated conversion of phosphorus containing organic waste, in which most of the phosphorus is captured in the humus material.
It is another object of the present invention to provide an improved process for the efficient, substantially odorless, biologically mediated transformation of organic wastes into suitable materials for recycling to the environment.
It is another object of the present invention to provide an improved process to create a biologically active, ecologically beneficial, substantially odorless humus material through the biologically mediated conversion of organic waste, particularly animal excrement.
It is a still further object of the present invention to create PAOs with the capability of accumulating significant levels of particulate phosphorus even when living in environments which have low concentrations of electron accepting substances (such as oxygen, nitrite, nitrate) with and/or without subjecting the PAOs to discrete anaerobic conditions in a physically defined and separate environment.
It is a still further object of the present invention to provide a process to create a biologically active, and/or nutrient rich, organic soil.
It is a still further object of the present invention to provide a process to create a biologically active, and/or nutrient rich, feed material or supplement.
These and other objects will be apparent from the following description of the invention.